1. Field of the Invention
The invention relates to improvements in techniques of manufacturing mineral fibers. More precisely, the invention relates to techniques in which the material of which the fibers are to be comprised is passed in the molten state into a hollow centrifuge having a large number of orifices at the periphery.
2. Background of the Prior Art
In techniques for the manufacture of mineral fibers, the material is expelled, under the action of centrifugal force, in the form of filaments which are passed into a gas flowing at high speed and at high temperature, with the said gas flow being along the peripheral wall of the centrifuge.
Such fiber production techniques are the subject of a very large number of publications. Among these one may cite Eur. Pat. Apps. Nos. 0 091 866 and 0 091 381.
It is seen from the prior literature, and particularly the above-cited two documents, that the qualities required for the fibers produced cover a wide range, depending on the intended uses of the fibers. Even among products not intended for use in acoustic or thermal insulation, there can be substantial differences.
The principal products of this type with regard to volume of production are felts known as "light felts" due to their low density. In order to achieve better thermal properties, these felts are advantageously comprised of very fine fibers (diameter &lt;5 microns).
Light felts have very limited resistance to compression. For other purposes, therefore, one prefers an insulation comprised of fibers which are less fine but more resistant to compression.
The above is just one example of differences in properties of products which may be demanded by users. Obviously, the production conditions will vary depending on the type of product sought.
The manufacturing techniques of the fibers in accordance with these requirements must satisfy criteria of productivity and production cost. Regardless of the product being produced, it is necessary to achieve the highest possible level of production, using a given installation, and at lowest cost.
These different considerations make it desirable to have available production equipment which can operate under very diverse sets of conditions.
Thus, the technique described in Eur. No. 0 091 381 proposes means of production of fibers having a set of insulating and mechanical properties which responds to most usual requirements. The fibers are produced at a high rate and are of a fine gauge. Their length is such that their arrangement in the felt is quite isotropic in the plane of receipt, and such that the felt has the required mechanical properties.
One may assume in general, other things being equal, that the resistance and strength of the felt are greater the greater the fiber length. ln order to obtain a homogeneous distribution of the fibers in the felt, however, it appears that they should be kept relatively short. However, these assumptions are not completely qeneral rules. The structure of the fibers themselves, and the fact that their individual characteristics are very similar, acts in a complex way to influence the insulating properties. Certain aspects of this will be discussed further, in connection with the applications of the invention.
Depending on the requirements, it is known to produce very fine, long fibers according to the techniques described in the above-cited documents. However, ordinarily in order to do this it is necessary to suffer a substantial reduction in the quantity produced by each installation.
It is also known to produce fine fibers at high production rates by, e.g., increasing the drawing effect by employing a hot gas flow. But ordinarily the fibers obtained are consequently shorter and less regular. lnsulation produced in this way has a relatively high density. It is used, e.g., for panels (called "roof panels") which are applied to flat roofs and which support covers, which covers provide sealing.
lt is therefore an object of the invention to provide means to enable diversity in the combinations of properties obtained by the techniques. In particular, the invention proposes to produce fibers which are fine and long, while maintaining high productivity of fibers on each installation, and without changing the chief characteristics of the centrifuge (number of orifices, dimensions of the centrifuge, etc.).